Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
Touch input devices or sensors for computers and other consumer electronics devices such as mobile phones, personal digital assistants (PDAs) and hand-held games are highly desirable due to their extreme ease of use. In the past, a variety of approaches have been used to provide touch input devices. The most common approach uses a flexible resistive overlay, although the overlay is easily damaged, can cause glare problems, and tends to dim an underlying display, requiring excess power usage to compensate for such dimming. Resistive devices can also be sensitive to humidity, and the cost of the resistive overlay scales quadratically with perimeter. Another approach is capacitive touch, which also requires an overlay. In this case the overlay is generally more durable, but the glare and dimming problems remain.
In yet another common approach, a matrix of infrared light beams is established in front of a display, with a touch detected by the interruption of one or more of the beams. Such ‘optical’ touch input devices have long been known (U.S. Pat. No. 3,478,220; U.S. Pat. No. 3,673,327), with the beams generated by arrays of optical sources such as light emitting diodes (LEDs) and detected by corresponding arrays of detectors (such as phototransistors). They have the advantage of being overlay-free and can function in a variety of ambient light conditions (U.S. Pat. No. 4,988,983), but have a significant cost problem in that they require a large number of source and detector components, as well as supporting electronics. Since the spatial resolution of such systems depends on the number of sources and detectors, this component cost increases with display size and resolution.
An alternative optical touch input technology, based on integrated optical waveguides, is disclosed in U.S. Pat. No. 6,351,260, U.S. Pat. No. 6,181,842 and U.S. Pat. No. 5,914,709, and in US Patent Application Nos. 2002/0088930 and 2004/0201579. The basic principle of such a device is shown in FIG. 1. In this optical touch input device, integrated optical waveguides (‘transmit’ waveguides) 10 conduct light from a single optical source 11 to integrated in-plane lenses 16 that collimate the light in the plane of a display and/or input area 13 and launch an array of light beams 12 across that display and/or input area 13. The light is collected by a second set of integrated in-plane lenses 16 and integrated optical waveguides (‘receive’ waveguides) 14 at the other side of the screen and/or input area, and conducted to a position-sensitive (i.e. multi-element) detector 15. A touch event (e.g. by a finger or stylus) cuts one or more of the beams of light and is detected as a shadow, with position determined from the particular beam(s) blocked by the touching object. That is, the position of any physical blockage can be identified in each dimension, enabling user feedback to be entered into the device. Preferably, the device also includes external vertical collimating lenses (VCLs) 17 adjacent to the integrated in-plane lenses 16 on both sides of the input area 13, to collimate the light beams 12 in the direction perpendicular to the plane of the input area.
The touch input devices are usually two dimensional and rectangular, with two arrays (X, Y) of transmit waveguides 10 along adjacent sides of the input area, and two corresponding arrays of receive waveguides 14 along the other two sides. As part of the transmit side, in one embodiment a single optical source 11 (such as an LED or a vertical cavity surface emitting laser (VCSEL)) launches light via some form of optical power splitter 18 into a plurality of waveguides that form both the X and Y transmit arrays. The X and Y transmit waveguides are usually fabricated on an L shaped substrate 19, and likewise for the X and Y receive waveguides, so that a single source and a single position-sensitive detector can be used to cover both X and Y dimensions. However in alternative embodiments, a separate source and/or detector may be used for each of the X and Y dimensions. For simplicity, FIG. 1 only shows four waveguides per side of the input area 13; in actual touch input devices there will generally be sufficient waveguides for substantial coverage of the input area.
These prior art devices house the waveguide structures that form the X and Y transmit arrays within a protective bezel that surrounds the input area. Typically, the input area will coincide with a display, in which case the touch input device may be referred to as a ‘touch screen’. Other touch input devices, sometimes referred to as ‘touch panels’, do not have a display. This disclosure applies to both types of input device. As will be appreciated, the bezel width necessarily limits the display size within a given touch screen device, which may be a significant limitation for small devices such as mobile phones. A further problem is that, to minimise the bezel width, the distance between the in-plane lenses and the external VCLs should be minimised, leading to a high magnification optical system that is extremely susceptible to errors in the design, fabrication and placement of the external VCLs.